The periodic formation of a domain inversion structure for forcibly inverting the polarization of ferroelectrics allows the implementation of optical frequency modulators utilizing surface acoustic waves, optical wavelength conversion devices utilizing the polarization inversion of nonlinear polarization, and the like. In particular, if the nonlinear polarization of nonlinear optical materials can be inverted periodically, high-efficiency wavelength conversion devices can be made; when light such as solid lasers is converted by using such devices, it will be possible to make small and lightweight short-wavelength light sources that can be applied for such fields as printing, optical information processing, and optical application measurement control.
As a method of forming a periodic domain inversion structure in a ferroelectric nonlinear optical material, so-called voltage application method is known. In this method, an interdigitated or comb-shaped electrode is formed on one main face of a ferroelectric single crystal substrate, a uniform electrode is formed on the other main face, and a pulse voltage is applied across both the electrodes. Such a method is described in Japanese Patent Publication Nos. H08-220578A, 2005-70195A and 2005-70194A.